Regulation of V-ATPase by Jasmonic Acid: Possible Role of Persulfidation.

Vacuolar H+-translocating ATPase (V-ATPase) is a proton pump crucial for plant growth and survival. For this reason, its activity is tightly regulated, and various factors, such as signaling molecules and phytohormones, may be involved in this process. The aim of this study was to explain the role of jasmonic acid (JA) in the signaling pathways responsible for the regulation of V-ATPase in cucumber roots and its relationship with other regulators of this pump, i.e., H2S and H2O2. We analyzed several aspects of the JA action on the enzyme, including transcriptional regulation, modulation of protein levels, and persulfidation of selected V-ATPase subunits as an oxidative posttranslational modification induced by H2S. Our results indicated that JA functions as a repressor of V-ATPase, and its action is related to a decrease in the protein amount of the A and B subunits, the induction of oxidative stress, and the downregulation of the E subunit persulfidation. We suggest that both H2S and H2O2 may be downstream components of JA-dependent negative proton pump regulation. The comparison of signaling pathways induced by two negative regulators of the pump, JA and cadmium, revealed that multiple pathways are involved in the V-ATPase downregulation in cucumber roots.

Involvement of NO in V-ATPase Regulation in Cucumber Roots under Control and Cadmium Stress Conditions.

Nitric oxide (NO) is a signaling molecule that participates in plant adaptation to adverse environmental factors. This study aimed to clarify the role of NO in the regulation of vacuolar H+-ATPase (V-ATPase) in the roots of cucumber seedlings grown under control and Cd stress conditions. In addition, the relationship between NO and salicylic acid (SA), as well as their interrelations with hydrogen sulfide (H2S) and hydrogen peroxide (H2O2), have been verified. The effect of NO on V-ATPase was studied by analyzing two enzyme activities, the expression level of selected VHA genes and the protein level of selected VHA subunits in plants treated with a NO donor (sodium nitroprusside, SNP) and NO biosynthesis inhibitors (tungstate, WO42- and N-nitro-L-arginine methyl ester, L-NAME). Our results indicate that NO functions as a positive regulator of V-ATPase and that this regulation depends on NO generated by nitrate reductase and NOS-like activity. It was found that the mechanism of NO action is not related to changes in the gene expression or protein level of the V-ATPase subunits. The results suggest that in cucumber roots, NO signaling interacts with the SA pathway and, to a lesser extent, with two other known V-ATPase regulators, H2O2 and H2S.

Interaction between the signaling molecules hydrogen sulfide and hydrogen peroxide and their role in vacuolar H+ -ATPase regulation in cadmium-stressed cucumber roots.

Vacuolar H+ -ATPase (V-ATPase; EC 3.6.3.14) is the main enzyme responsible for generating a proton gradient across the tonoplast. Under cadmium (Cd) stress conditions, V-ATPase activity is inhibited. In the present work, hydrogen sulfide (H2 S) and hydrogen peroxide (H2 O2 ) cross-talk was analyzed in cucumber (Cucumis sativus L.) seedlings exposed to Cd to explain the role of both signaling molecules in the control of V-ATPase. V-ATPase activity and gene expression as well as H2 S and H2 O2 content and endogenous production were determined in roots of plants treated with 100 µM CdCl2 and different inhibitors or scavengers. It was found that H2 S donor improved photosynthetic parameters in Cd-stressed cucumber seedlings. Cd-induced stimulation of H2 S level was correlated with the increased activities of the H2 S-generating desulfhydrases. Increased H2 O2 and lowered H2 S contents in roots were able to reduce V-ATPase activities similar to Cd. H2 O2 and H2 S-induced modulations in V-ATPase activities were not closely related to the transcript level of encoding genes, suggesting posttranslational modifications of enzyme protein. On the other hand, exogenous H2 O2 raised H2 S content in root tissues independently from the desulfhydrase activity. Although treatment of control plants with H2 S significantly stimulated NADPH oxidase activity and gene expression, H2 S did not affect H2 O2 accumulation in roots exposed to Cd. The results suggest the existence of two pathways of H2 S generation in Cd-stressed cucumber roots. One involves desulfhydrase activity, as was previously demonstrated in different plant species. The other, the desulfhydrase-independent pathway induced by H2 O2 /NADPH oxidase, may protect V-ATPase from inhibition by Cd.

Phosphate Uptake and Allocation - A Closer Look at Arabidopsis thaliana L. and Oryza sativa L.

This year marks the 20th anniversary of the discovery and characterization of the two Arabidopsis PHT1 genes encoding the phosphate transporter in Arabidopsis thaliana. So far, multiple inorganic phosphate (Pi) transporters have been described, and the molecular basis of Pi acquisition by plants has been well-characterized. These genes are involved in Pi acquisition, allocation, and/or signal transduction. This review summarizes how Pi is taken up by the roots and further distributed within two plants: A. thaliana and Oryza sativa L. by plasma membrane phosphate transporters PHT1 and PHO1 as well as by intracellular transporters: PHO1, PHT2, PHT3, PHT4, PHT5 (VPT1), SPX-MFS and phosphate translocators family. We also describe the role of the PHT1 transporters in mycorrhizal roots of rice as an adaptive strategy to cope with limited phosphate availability in soil.